The Fremennik Slayer Dungeon is a dungeon located south-east of Rellekka, featuring monsters that can only be killed by those adept in the Slayer skill. The monsters get progressively stronger as the player goes deeper into the dungeon. It was released during the Slayer skill update on 26 January2005.

Note: Everything but the kurask and cave crawlers are unaggressive (although the cave crawlers are only aggressive to players with a combat level of 46 and below). Dwarf multicannons cannot be used in this dungeon because the air in the tunnel is too "humid".

This dungeon contains several Slayer monsters each with its own chamber.

The first chamber contains eight cave crawlers (level 10 Slayer is required to kill them). They are level 76 and 106. This chamber also contains an Agility shortcut which, at level 81 Agility, can be used to enter the pyrefiend area.

The second chamber contains seven rockslugs - level 20 Slayer and a bag of salt are required to kill them. These are level 70.

The third chamber contains seven cockatrice. They require level 25 Slayer and a mirror shieldor a Mask of Stone/Reflection - without one, the player's stats (including life points) will be dangerously reduced. They commonly drop level 2 clue scrolls. These are level 44.

A shortcut to the pyrefiend room

The fourth chamber contains thirteen pyrefiends which can be killed at level 30 Slayer. They attack with magic; therefore, wearing dragonhide or other high magic defence armour would be wise. The Agility shortcut here requires level 81 Agility, and leads back to the first chamber. Like cockatrice, these also drop level 2 clue scrolls. They are level 88 and 96.

The fifth chamber contains eight basilisks which require level 40 Slayer and a mirror shield or Mask of Stone/Reflection to kill. There is a small safe spot against the south-east wall. (The safespot spans multiple squares, and can be utilised by standing directly adjacent to the zigzag pattern.) From there, a player can safely attack any basilisk to the north. Engaging with a southern basilisk will allow them to reach the player. With level 62 Agility the player can use the agility shortcut to enter the turoth chamber. These, like cockatrices and pyrefiends, drop level 2 clue scrolls. They are level 77.

The sixth chamber contains ten jellies, which require level 52 Slayer to kill. They use ranged attacks, so melee armour is recommended. All monsters beyond and including these can drop level 3 Clue scrolls. These are level 68.

The eighth chamber contains five kurask. They require 70 Slayer to kill. Like Turoths, they are immune to all damage not dealt via a leaf bladed spear, a leaf-bladed sword, broad arrows, broad-tipped bolts, or the Slayer Dart spell. These are level 112, and are aggressive to all players.

The ninth and final chamber contains nine aquanites. They require level 78 Slayer to kill, and have the ability to turn off a player's protection prayer. They can drop an amulet of ranging. Aquanites are not aggressive. These are level 136.

When examining the cave entrance from the outside, the game text used to read, "Wow - it's a guinea pig! No, hang on, it's a cave." - a pun on "cavie". Now it reads, "It leads to a small cave."

The layout of the dungeon is backwards. One enters by walking east but then to progress through the caves, the player must go west.

Most of the monsters drop white/gold parts of the mystic set.

When the slayer cave was first introduced, it was only possible to get further into the cave using agility shortcuts. Thus, a player could get stuck after using an agility potion, followed by the effect fading.